neo4j - Relationship between three nodes

Question

I'm totally new to Neo4j and I'm testing it in these days. One issue I have with it is how to correctly implement a relationship which involves 3 different nodes using Spring Data. Suppose, for example, that I have 3 @NodeEntitys: User, Tag and TaggableObject.

As you can argue, a User can add a Tag to a TaggableObject; I model this operation with a @RelationshipEntity TaggingOperation. However, I can't find a simple way to glue the 3 entities inside the relationship. I mean, the obvious choice is to set @StartNode User tagger and @EndNode TaggedObject taggedObject; but how can I also add the Tag to the relationship?

Answer 1

This is called a "hyperedge", I believe, and it's not something that Neo4j supports directly. You can create an additional node to support it, tough. So you could have a TagEvent node with a schema like so:

(:User)-[:PERFORMED]->(:TagEvent)
(:Tag)<-[:USED]-(:TagEvent)
(:TagObject)<-[:TAGGED]-(:TagEvent)

Another alternative is to store a foreign key as a property on a relationship or a node. Obviously that's not very graphy, but if you just need it for reference that might not be a bad solution. Just remember to not use the internal Neo4j ID as in future versions that may not be dependable. You should create your own ID for this purpose.